Particularly in mobile radio, there is the trend toward “multiband” receivers, which are designed to receive radio signals on different frequency bands. In Germany, for example, there are two different frequency bands for the GSM (Global System for Mobile communication) mobile radio standard, namely 900 MHz and 1 800 MHz. While the “D networks” operate in the frequency range around 900 MHz, the “E networks” have an associated frequency range around 1 800 MHz. Mobile radios which can send and receive on both frequency levels are called dual-band appliances.
In order to allow mobile radios to be used worldwide within the context of the globalization of the markets and the high level of user mobility, it is desirable for just one appliance to be provided with access not just to the frequency ranges around 900 and 1 800 MHz but also to other frequency ranges, such as GSM 1 900 and GSM 800, as are used in the USA, for example.
In the reception signal paths of such mobile radio receivers, there is now the problem of designing channel filters, amplifiers etc. to be suitable for these various frequency bands. Multiband receivers are normally designed such that a separate reception path is provided for each reception band. This reception path comprises not only a channel filter but also a specially adapted low noise preamplifier, and also a separate down-conversion frequency mixer.
The documents WO 02/27953, U.S. Pat. No. 6,029,052 and U.S. Pat. No. 6,405,025 each describe different embodiments of receivers. Each receiver contains a plurality of parallel receiver paths with a respective low noise amplifier. The outputs of the amplifiers, which are isolated from one another, are coupled to a jointly used radio-frequency mixer. Each amplifier is designed to amplify a signal predetermined by a mobile radio standard.
A drawback of such a receiver architecture is the relatively high component complexity and the associated area involvement for integrating such circuits.